Reply to the 'Comment on "Unravelling the kinetics, isotherms, thermodynamics, and mass transfer behaviours of Zeolite Socony Mobil - 5 in removing hydrogen sulphide resulting from a dark fermentative biohydrogen production process"' by K. H. Chu, M. A. Hashim and M. Hafiz Zawawi, Phys. Chem. Chem. Phys., 2025, 27, DOI: 10.1039/D4CP04682J.

In this reply, we address the concerns raised regarding the theoretical consistency of the modeling approaches used in our original study on hydrogen sulfide adsorption onto ZSM-5. Specifically, the issues relate to the application of the Temkin isotherm, the Weber-Morris intraparticle diffusion model, and the use of a dimensional distribution coefficient in the thermodynamic analysis. We acknowledge that the simplified Temkin model was misapplied and does not strictly conform to theoretical requirements; however, it was used to represent mid-range adsorption behavior consistent with our experimental conditions. The inclusion of an intercept in the Weber-Morris model is defended as a diagnostic feature that reveals the contribution of boundary layer resistance, which is relevant in fixed-bed gas-solid systems. The use of a dimensional coefficient Kd = qe/Ce in thermodynamic calculations is justified based on its practicality in real gas-phase systems where activity-based constants are not easily defined. Collectively, while theoretical refinements are acknowledged, the main findings of the original study remain robust and well-supported by the experimental evidence. In addition, the opportunities for further refinement in isotherm fitting and thermodynamic calculations are acknowledged, and directions for future work are outlined.